This is about as simple as it gets.

To use:

• Build with make
• Load with insmod example.ko
• Check output in kernel buffer with dmesg
• See the module loaded in lsmod | grep example
• Unload with rmmod example.ko
• Check the second output in the kernel buffer with dmesg

Alternatively:

• Run make test and observe the two outputs as the module is loaded/unloaded.

NOTE: You'll need build-essential and linux-headers-$(uname -r) installed.

Followed along from here.